The invention relates to a method of operating an internal combustion engine in particular an auto-ignition internal combustion engine with direct fuel injection including a cylinder with a cylinder head having inlet and outlet valves and a piston movably disposed in the cylinder.
In direct-injection internal combustion engines with auto-ignition, lean homogeneous fuel/air mixtures are often made to auto-ignite so that high efficiency levels and improved exhaust emissions are obtained. In such internal combustion engines which are referred to as HCCI or PCCI internal combustion engines, that is, internal combustion engines with compression ignition, a lean basic mixture of air, fuel and retained exhaust gas is generally formed at partial load and auto-ignited. During full load engine operation, a stoichiometric mixture is frequently formed and spark ignited because, at high loads, steep rises in pressure could occur in the combustion chamber due to the auto-ignition which would adversely affect the operation of the engine.
According to the current state of the art, selective control of the compression ignition combustion described above can be achieved only with difficulty since the time of auto-ignition depends very greatly on the operating parameters of the engine and the ambient conditions. Furthermore, optimizing the combustion in terms of the exhaust gas temperatures can be made more difficult in particular as a result of the various features triggering the ignition. A better efficiency level is achieved however with compression ignition than with spark ignition.
It is the object of the present invention to provide a method of operating an internal combustion engine in which an operating mode which is optimized in terms of efficiency is ensured both in an auto-ignition mode and in a spark ignition mode.